MERISTIC PHENOMENA 33 



readily distinguishable. There is the event by which the cell 

 divides, and the event by which the two halves or their descend- 

 ants are or may be differentiated. It is common knowledge that 

 in some cell-divisions two similar halves, indistinguishable in 

 appearance, properties, and subsequent fate, may be produced, 

 while in other divisions daughter-cells with distinct properties 

 and powers are formed. We cannot imagine but that in the 

 first case, when the resulting cells are idenfical, the division 

 is a mechanical process by which the mother-cell is simply 

 cut in two; while in order that two differentiated halves may be 

 produced, some event must have taken place by which a chemical 

 distinction between the two halves is effected. 1 In any ordinary 

 Mendelian case we have a clear proof that such a chemical dif- 

 ference may be established between germ-cells. The facts of 

 colour-inheritance for instance prove that germ-cells, otherwise 

 identical, may be formed possessing the chromogen-f actor which 

 is necessary to the formation of colour in the flowers, or destitute 

 of that factor. Similarly the germ-cells may possess the ferment 

 which, by its action on the chromogenic substance, produces 

 the colour, or they may be without that ferment. The same 

 line of argument applied to a great range of cases. Nevertheless, 

 though differences in chemical properties are often thus consti- 

 tuted by cell-divisions, and though we are thus able to make a 

 quasi-chemical analysis of the individual by determining and 

 enumerating these properties, yet it is evident that the dis- 

 tribution of these factors is not itself a chemical process. This 

 is proved by the fact that similar divisions may be effected be- 

 tween halves which are exactly alike, and also by the fact that 

 the numbers in which the various types of germ-cells are formed 

 negative any suggestion of valency between them. The recog- 

 nition of the unit-factors may lead indeed must lead to great 

 advances in chemical physiology which without that clue would 

 have been impossible, but in causation the chemical phenomena 

 of heredity must be regarded as secondary to the physical or 



1 In saying this we make no assumption as to the particular cell-division at 

 which differentiation occurs. This may be one of the maturation-divisions, or it 

 may perhaps be much earlier. 



